Leveling instrument

ABSTRACT

A leveling instrument has an image-forming objective, a picture-taking spatial resolution optoelectronic detector, and electronics and a computing unit for driving the detector and evaluating the detector signals. The image-forming objective is subdivided into several zones of field depth designed each as a different aperture plate. Corresponding partial zone of the detector are associated to the aperture plate. The partial zones of the detector may also be designed as individual spatial resolution detectors. Since all level indicators, whatever their distance from the levelling instrument, may be sensed in one of the zones of field depth designed as aperture plates and reproduced by said aperture plate, the image-forming objective need not be manually or automatically refocused nor aligned with respect to the target.

BACKGROUND

The invention relates to a leveling instrument having an imaging opticalsystem and a spatially resolving opto-electronic detector for imagerecording, and having an electronic system and an arithmetic unit forcontrolling the detector and for image evaluation.

Devices of the said type are disclosed in German Publication DE 34 24806 C2 and U.S. Pat. No.4,715,714. The leveling instrument describedthere determines the distance and the height difference relative toleveling rods set up at a distance. It therefore serves in geodeticsurveying for determining benchmarks and for topographic andcartographic surveying. However, it is also used in constructionsurveying, in building traffic ways or in building tunnels and inmining.

In the classic leveling instrument, its telescope is used by theoperator for the purpose of visually reading off the numerical value ona height scale of the leveling rod. The numerical value read off islocated exactly on the optical axis in the cross hairs of the telescope.

The advent of automated digital leveling instruments rendered itpossible for the first time to read off rods electronically. For thispurpose, a leveling rod has been developed on which a code patterncomposed of black and white elements is applied. In accordance with DE34 24 806 C2, the portion of the code pattern situated in the field ofview of the telescope optical system of the digital leveling instrumentis imaged on a spatially resolving optoelectronic detector group. Inthis process, use is made not only of the code pattern informationlocated on the optical axis of the telescope, but also of the codepattern information located in the entire field of view of thetelescope, in order to determine the height value. In addition, theposition sensor of the focusing device of the digital levelinginstrument supplies the approximate distance from the leveling rod. Theexact distance is determined by the evaluation procedure of the recordedcode pattern.

The leveling operation runs as follows. The leveling rod is sightedusing the telescope of the leveled leveling instrument, and focusedusing the focusing device. The position sensor of the focusing devicesupplies the distance from the leveling rod, from which, together withthe focal length of the telescope objective, the distance scale iscalculated. This distance scale is included in the code pattern, inorder to be able to carry out a comparison with a reference codepattern. The latter is located as an original code pattern of theleveling rod in an electronic memory. A cross correlation whichdetermines a best possible agreement of the measured code patternsection with a corresponding section on the reference code pattern iscarried out as comparison method. The agreement found reveals thesighted location on the leveling rod, and thus the height of theleveling rod with respect to the leveling instrument.

Although the actual leveling and measuring operation is performed fullyautomatically, it is necessary for the imaging optical system of theleveling instrument to be set in advance such that the leveling rod issharply imaged in the intermediate image plane of the telescopeobjective. For this purpose, a focusing lens can be mechanicallydisplaced along the optical axis of the telescope optical system. Thefocusing lens is firmly connected to a focusing drive. The focusingdrive is actuated manually and at the same time the image of theleveling rod is observed through the telescope eyepiece. The focusingoperation is terminated when the image of the leveling rod appearssharp.

An electronic leveling instrument of the said type is also described inEP 0 576 004 A1. A telescope is used as imaging optical system. Thetelescope is focused onto a leveling rod whose distance and height areto be determined with respect to the leveling instrument. A black andwhite pattern of lines is applied to the leveling rod. The objective ofthe telescope picks up that part of the pattern of lines of the levelingrod which is located in its field of view, and generates therefrom animage on a photoelectric receiver. The electric signals of the receiverare evaluated in a signal processor directly or via a Fouriertransformation. In the process, the distance between the levelinginstrument and leveling rod, and the leveling height are determined fromthe period and from the phase of the pattern of lines picked up by thetelescope objective and evaluated by the photoelectric device.

The focusing of the telescope onto the leveling rod is performedmanually. For this purpose, a focusing lens is displaced along theoptical axis of the telescope until the image of the leveling rodobserved through the telescope eyepiece appears sharp.

in another design, the focusing lens is motorized, and this rendersautomated focusing possible. In this case, the focusing lens is moved insteps with the aid of a motor control. With each step, the detectorrecords the pattern of lines of the leveling rod, and the signalprocessor forms the Fourier transform therefrom. The height of the peak,corresponding to the periodic structure of the pattern of lines, of theFourier transform is a measure of the focusing. The maximum peak heightof this Fourier transform signifies optimum focusing. Consequently, thefocusing lens is brought to this position after passing through themaximum peak height.

The two digital leveling systems according to DE 34 24 806 C2 and U.S.Pat. No. 4,715,714 and to EP 0 576 004 A1 require moving optical andmechanical components to focus the leveling rod. Such components, whichare moved mechanically in relation to one another, have to be producedand adjusted with care. This complicates production and increases cost.

In addition, the manual focusing is somewhat troublesome for the user ofthe leveling instrument: the user has to look through the eyepiece ofthe telescope and subjectively estimate the focusing of the leveling rodimage. Although the motorized version of the focusing lens relieves theuser of this work, this is achieved at the expense of a high outlay formeasurement. Thus, the leveling rod image must be recorded by thedetector and processed in a microprocessor with the aid of suitablealgorithms. The computational result must be converted by an electronicmotor control, the electric motor must be driven, and the focusing lensmust be moved to the appropriate position. The position must be knownvia a position sensor or, in the case of the use of a stepping motor, atleast via the counting steps, in order to be able to move back to thisposition again after passing through the optimum focusing position.Moreover, the probability of the failure of an instrument is increasedby the additional extent of software, electronics and, in particular,electromechanics, because of the finite service life of the electricmotor.

SUMMARY OF THE INVENTION

Consequently, it is an object of the invention to develop a levelinginstrument which sharply images a leveling rod set up at any desireddistances without refocusing and without mechanical adjustment.

This object is achieved according to the invention when, for the purposeof producing sharp images from different distance ranges, the imagingoptical system has at least two differently imaging pupil zonessimultaneously examining different distance ranges.

Advantageous developments and improvements of the invention arecharacterized by the features described below.

In the invention, or object located at a specific distance is imaged inthe conjugate intermediate image plane of a telescope when the latter isfocused. Each point of the object is imaged in a punctiform fashion. Thepoints of other objects which are situated nearer to or further from thetelescope produce circles of confusion in the intermediate image planesof the telescope. The diameters of these circles turn out larger thefurther the object is removed from the focused object plane. In the casein which the diameters of the circles of confusion remain smaller thanthe distance between the light-sensitive structures of a spatiallyresolving detector arranged in an intermediate image plane, the detectorrecords the areas of the circles of confusion as points. Under thiscondition of the maximum permissible diameter of the circles ofconfusion, the imaging equation yields a specific distance range, whichthe detector images sharply. This distance range, referred to as thedepth of field, is larger the larger the distances between thelight-sensitive elements of the detector, that is to say the poorer theresolving power of the latter.

It is normal to use linear diode rows of two-dimensionalposition-sensitive CCD arrays as position-sensitive optoelectronicdetectors for the digital leveling instruments. Said arrays receive theimage of the leveling rod via a beam splitter arranged in the beam pathof the telescope. Because of the beam splitting, said beam splitterpermits simultaneous observation of the leveling rod via the telescopeeyepiece. During observation of the leveling rod through the telescopeeyepiece, with its discrete light-sensitive elements, the observer'sretina serves as the position-sensitive detector. Thus, the resolvingpower of the eye contributes to the depth of field of the objects seenby the observer.

In addition to the resolving power of the detector, the data for theoptical system used also features in the determination of the depth offield. Thus, it is generally known that when the f-number is high thedepth of field is also high. Thus, a role is also played by the size ofthe aperture stop, the focal length of the telescope objective, and alsothe distance from the object itself. Geometrical objective aberrationsand diffraction effects also exert an additional influence.

Thus, overall the depth of field of an electronic leveling instrument isdetermined by the objective used and the detector used. If the levelingrod is located at a distance outside the instantaneously set distanceincluding its associated depth of field, it is necessary to use afocusing lens to refocus in the conventional way described above and toset a different distance range at the leveling instrument. In accordancewith the present invention, this setting is eliminated and all thedevices bound up therewith are eliminated. The maximum (possiblyinfinite) distance of the leveling rod is split into individual distanceranges which, according to the invention, are assigned to the depths offield of the differently imaging pupil zones of the imaging opticalsystem. An imaging optical system configured in such a way receives thelight coming from the leveling rod with each of its imaging pupil zones,and generates a complete image of the leveling rod. However, only one ofthese imaging pupil zones images the leveling rod sufficiently sharplyto enable an evaluation. The leveling rod is then located precisely inthe depth of field of this imaging zone.

The differently imaging pupil zones according to the invention of theimaging optical system, which are assigned to the different distanceranges, can be realized in different ways. In the simplest case,individual apertures are arranged separately next to one another. Theycan have aperture areas of different size for the light admission, andfocal lengths or image distances of different size. Refractive and/ordiffractive optical elements are used as imaging elements. Theindividual apertures can be represented by conventional objectives withexplicitly refractive elements whose different refractive powers signifycorresponding focal lengths. These are tuned to one another in such away that they sharply image all desired distances between the levelinginstrument and leveling rod. Each objective focuses the objects(leveling rod) of its depth of field on to a single spatially resolvingdetector assigned to it or, via beam deflection, on to a subregion,assigned to it, of a common spatially resolving detector. In order stillto receive an adequate quantity of light from objects further removed,the appropriate objectives are frequently equipped with a largeraperture area.

A differently designed version of the subject matter of the inventioncomprises a substantially more compact design with only a singleaperture which is itself split into individual, differently imagingpupil zones. Here, as well, each pupil zone has a different focal lengthand/or imaging distance. Corresponding to these in accordance with theimage equation, and taking account of the circles of confusion, arespecific distance ranges which are imaged sharply onto the assigneddetectors or the assigned subregions of a common detector. If the focallengths of the individual pupil zones are of the same size, differentfocal lengths are selected in accordance with the distance ranges, andindividual detectors are arranged in the image planes.

The individual pupil zones of the aperture can be designed in arotationally symmetrical fashion relative to an axis. However, this isnot a necessary condition, and so the pupil zones can also have apertureareas of any size and any shape. The imaging characteristics arerealized by refractive or by diffractive optical elements, or also by acombination of these types of imaging.

Small openings signify large depths of field. However, this can giverise to intensity problems. Thus, active illumination of the levelingrod may be required for radiometric reasons. The illumination is bestperformed using a spotlight. The illumination beam path can be guided bybeing reflected in via a beam splitter and guided through the imagingpupil zones. It is also possible for a spotlight to be integrated intothe leveling instrument independently of the apertures, or to be mountedon the leveling instrument. A light-emitting diode or laser diodeemitting in the near infrared can serve as radiation source, forexample. Many optoelectronic detectors are particularly sensitive inthis wavelength region.

The differently imaging pupil zones of an aperture, or a group ofdifferently imaging separately arranged apertures cover the entirerelevant distance range for an electronic leveling instrument by virtueof their depths of field. In mathematical terms, the large depth offield is achieved by a suitable spatial configuration of the opticalpupil function which is yielded from the distribution of the complexwave amplitudes in the exit pupil. The waves coming from there arerecorded by the spatially resolving detectors as an intensitydistribution which is processed in the downstream evaluation electronicsystem and with the aid of the evaluation software. The intelligentevaluation of the detector signals detects the respective optimumimaging zone.

The result of all the distance ranges simultaneously detected by theimaging optical system is a range of advantages both for producing theleveling instrument and for the leveling operation itself. Thus, theworking operation of prior focusing by the user is eliminated in eachleveling measurement. There is no longer a need to look through aneyepiece or to undertake focusing. The operation of the electronicleveling instrument is simplified thereby.

The focusing lens and the focusing drive are no longer required. Thisrenders their production, assembly and adjustment superfluous, therebysaving costs. Since, in addition, the user no longer has to look throughthe eyepiece of the telescope, the production, assembly and adjustmentof the telescope eyepiece and of the beam splitter assigned to it arerendered superfluous. This beam splitter served to split the beam pathin the telescope for the purpose of producing an image both on theoptoelectronic detector and on the observer's retina. The leveling rodcan be sighted approximately using substantially simpler means such as,for example, marking alignment lines on the leveling instrument, or asimple auxiliary telescope.

By comparison with a leveling instrument having automated focusing bymeans of a motorized focusing lens, the motorizing superstructures andmotor, including its electronic drive, are also eliminated. Movingmechanical and optical components are no longer present. With a fixedgeometrical arrangement of the imaging optical system and of thedetector or plurality of detectors, the leveling instrument according tothe invention has a simple and robust design.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are explained below in moredetail with the aid of the drawing, in which:

FIG. 1 shows a diagrammatic representation of a leveling instrument withan imaging optical system having individual apertures and havingindividual detectors assigned to them,

FIG. 2 shows a diagrammatic representation of a leveling instrument withan imaging optical system having individual apertures and having acommon detector,

FIG. 3 shows a diagrammatic representation of a leveling instrument withan aperture split into pupil zones and having reflective opticalelements and individual detectors,

FIG. 4 shows a diagrammatic representation of the front view of theleveling instrument from FIG. 3,

FIG. 5 shows a diagrammatic representation of a leveling instrument withan aperture split into pupil zones, having refractive optical elementsand having a diffractive correction element,

FIG. 6 shows a diagrammatic representation of a leveling instrument witha diffractive optical element, split into pupil zones, as an imagingoptical system, and

FIG. 7 shows a diagrammatic representation of a leveling instrument withan aperture split into pupil zones and a common detector.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Objectives 1 to 4 of the leveling instrument 10 are representeddiagrammatically in FIG. 1 as individual apertures. The objectives 1 to4 have aperture areas of different size with diameters D1, D2, D3, D4,and permanently set focal lengths of different size, which are indicatedby different thicknesses of the objectives. Spatially resolvingoptoelectronic detectors 5 to 8 are arranged at different, permanentlyset distances (image distances) from the respective assigned objectives1 to 4. Each objective/detector pair (1 and 5, 2 and 6, 3 and 7, 4 and8) images objects in its depth of field. The depths of field are tunedto one another in this case such that they produce a coherent distancerange which reaches up to a maximum distance from the levelinginstrument 10. The maximum distance can also be infinite.

A leveling rod located within the maximum distance is sharply imaged andrecorded by that one of the objective detector pairs (1 and 5, 2 and 6,3 and 7, 4 and 8) in whose depth of field the instantaneous distance ofthe leveling rod falls. The electronic system 40 controls the detectors5 to 8 and receives and processes their signals. The arithmetic unit 41connected to the electronic system 40 executes the control andevaluation software. The evaluation determines the optimum imaging ofthe leveling rod. The image of the leveling rod is then furtherprocessed in order to determine leveling data, account also being taken,in particular, of an offset of the axis of the measuring system from areference axis of the instrument, and of the optimization of thedistance within the depth of field. The electronic system 40 and thearithmetic unit 41 are integrated in the leveling instrument 10. Thearithmetic unit 41 can also be accommodated outside the levelinginstrument 10.

In FIG. 2, the subregions 9a to 9d of a single spatially resolvingoptoelectronic detector 9 replace the individual detectors 5 to 8 ofFIG. 1. The electronic system 40' and the software know the assignmentof the subregions 9a to 9d to the objectives 1 to 4. Arranged in thebeam paths between the objectives 1 to 4 and the detector 9 arebeam-deflecting elements which are represented by way of example asprisms 51 to 54 in FIG. 2. They serve to guide beams between theindividual objectives 1 to 4 and the subregions 9a to 9d of the detector9. The principle of the mode of operation of the leveling instrument 11according to FIG. 2 is identical to that of the leveling instrument 10in FIG. 1, and is described with reference to FIG. 1.

A different optical design is exhibited by the leveling instrument 12 inFIG. 3. Instead of individual, separately arranged apertures,differently imaging pupil zones 21, 22 and 23 are grouped together inone aperture 20. The pupil zones 21, 22 and 23 comprise refractiveoptical elements of different refractive power and thus of differentfocal lengths. In this exemplary embodiment, the image distances arekept to the same size, and use is made of individual detectors 5, 6 and7 assigned to the pupil zones 21, 22 and 23. The different depths offield of the pupil zones 21, 22 and 23 together yield the possibledistance range within which a leveling rod is sharply imaged on one ofthe detectors. As in the previous figures, the electronic system 40 andthe arithmetic unit 41 have the purpose of detector control and imageevaluation.

FIG. 4 shows a front view of the leveling instrument 12 of FIG. 3. Forthe light admission, the pupil zones 21, 22 and 23 have aperture areaswhich are of different size and are differently shaped. Because of itslarger aperture area, the pupil zone 23 also collects a larger quantityof light. As a result, lower light intensities owing to a leveling rodset up at greater distances are compensated at least in part.Consequently, pupil zones with larger aperture areas are designed forlarger distance ranges.

In order simultaneously to obtain a compact design of the imagingoptical system 20, the aperture areas of the pupil zones 21, 22 and 23abut one another as optimally as possible, resulting in differentshapes. Going beyond the pupil zones 21, 22 and 23 represented in FIG. 3and FIG. 4, it is possible by means of a different split or by extensionto produce a larger number of aperture areas. In turn, the latter areassigned individual detectors or detector areas of a common detector inaccordance with the arrangement of the aperture areas.

In FIG. 5, the imaging optical system 20 of the leveling instrument 13differs from the imaging optical system 20 of the leveling instrument 12from FIG. 3 by an additionally mounted diffractive optical element 29.The diffractive optical element 29 corrects the images produced by therefractive pupil zones 21, 22 and 23. It can be produced from a glassplate on whose surface diffractive structures are vapor-deposited, orare etched into the surface. Such structures can also be applieddirectly to the refractive pupil zones 21, 22 and 23.

In FIG. 6, the imaging optical system of the leveling instrument 14comprises exclusively a diffractive optical system 30. The diffractiveoptical system 30 is also split into different pupil zones 31, 32 and33, which image different depths of field onto the correspondinglyassigned detectors 5, 6 and 7 by diffraction.

Finally, an imaging optical system 20 as in FIG. 5 and a detector 9 asin FIG. 2 are represented in FIG. 7. The subregions 9a, 9b and 9c of thedetector 9 are here assigned to the differently imaging pupil zones 21,22 and 23. The prisms 55 and 56 serve as beam-deflecting elements of thebeam guidance between the pupil zones 21, 22 and 23 and the detectorregions 9a, 9b and 9c.

An electronic system 40' and an arithmetic unit 41 are connecteddownstream of the detector 9 for the purposes of control and evaluation.In addition, a spotlight 60 is provided for illuminating the object tobe recorded, and is integrated in the leveling instrument 15. The lightsource 61 of the spotlight 60 can be a laser diode emitting in theinfrared.

We claim:
 1. A leveling instrument having an imaging optical system(1-4; 20) and a spatially resolving optoelectronic detector (5-8; 9),and having an electronic system (40; 40') and an arithmetic unit (41)for controlling the detector and for image evaluation, wherein for thepurpose of producing sharp images from different distance ranges theimaging optical system (1-4; 20) has at least two differently imagingpupil zones (1-4; 21-23) simultaneously imaging light from differentdistance ranges and wherein the detector simultaneously receivesspatially separated images from the at least two differently imagingpupil zones.
 2. An instrument according to claim 1, wherein thedifferently imaging pupil zones (1-4; 21-23) have permanently set focallengths of different size.
 3. An instrument according to claim 1,wherein the differently imaging pupil zones (1-4; 21-23) havepermanently set image distances of different size.
 4. An instrumentaccording to claim 1, wherein the differently imaging pupil zones (1-4;21-23) have permanently set focal lengths of the same size, butpermanently set image distances of different size.
 5. An instrumentaccording to claim 1, wherein the differently imaging pupil zones (1-4;21-23) have aperture areas (D1, D2, D3, D4; 21, 22, 23) of differentsize.
 6. An instrument according to claim 1, wherein the differentlyimaging pupil zones (1-4; 21-23) have aperture areas (D1, D2, D3, D4;21, 22, 23) of different shape.
 7. An instrument according to claim 1,wherein the differently imaging pupil zones (1-4) are formed byindividual, separately arranged apertures (1-4).
 8. An instrumentaccording to claim 1, wherein the differently imaging pupil zones(21-23) are formed together in a single aperture (20).
 9. An instrumentaccording to claim 1, wherein the differently imaging pupil zones (1-4;21-23) are formed by refractive (21, 22, 23) and/or diffractive (29; 30)optical elements.
 10. An instrument according to claim 1, wherein thespatially resolving optoelectronic detector includes a plurality ofspatially resolving detectors and wherein the differently imaging pupilzones (1-4; 21-23) are respectively assigned to one of the plurality ofspatially resolving detectors (5-8).
 11. An instrument according toclaim 1, wherein the differently imaging pupil zones (1-4; 21-23) arerespectively assigned to a subregion (9a-9d) on the spatially resolvingoptoelectronic detector (9).
 12. An instrument according to claim 11,wherein the assignment is performed by beam-deflecting optics (51-54).13. An instrument according to claim 12, wherein the beam-deflectingoptics are prisms (51-54).
 14. An instrument according to claim 1,further comprising an integrated spotlight (60) for illuminating theobject to be imaged.
 15. An instrument according to claim 14, whereinthe light source (61) of the spotlight (60) is a laser diode (61).
 16. Aleveling instrument to determine distance relative to a leveling rod,the leveling instrument comprising:an imaging optical system, theimaging optical system having at least two differently imaging pupilzones for simultaneously imaging light from at least two differentdistance ranges; a spatially resolving optoelectronic detector tosimultaneously receive spatially separated images from said at least twodifferently imaging pupil zones of the imaging optical system; and anelectronic system and arithmetic unit to control the detector and toevaluate images from the detector.
 17. An instrument according to claim16, wherein the differently imaging pupil zones have permanently setfocal lengths of different size.
 18. An instrument according to claim16, wherein the differently imaging pupil zones have permanently setimage distances of different size.
 19. An instrument according to claim16, wherein the differently imaging pupil zones have permanently setfocal lengths of the same size, but permanently set image distances ofdifferent size.
 20. An instrument according to claim 16, wherein thedifferently imaging pupil zones have aperture areas of different size.21. An instrument according to claim 16, wherein the differently imagingpupil zones have aperture areas of different shape.
 22. An instrumentaccording to claim 16, wherein the differently imaging pupil zones areformed by individual, separately arranged apertures.
 23. An instrumentaccording to claim 16, wherein the differently imaging pupil zones areformed together in a single aperture.
 24. An instrument according toclaim 16, wherein the differently imaging pupil zones are formed by atleast one of refractive optical elements and diffractive opticalelements.
 25. An instrument according to claim 16, wherein the spatiallyresolving optoelectronic detector includes a plurality of spatiallyresolving detectors and wherein the differently imaging pupil zones arerespectively assigned to one of the plurality of spatially resolvingdetectors.
 26. An instrument according to claim 16, wherein thedifferently imaging pupil zones are respectively assigned to a subregionon the spatially resolving optoelectronic detector.
 27. An instrumentaccording to claim 26, wherein the assignment is performed bybeam-deflecting optics.
 28. An instrument according to claim 27, whereinthe beam-deflecting optics includes prisms.
 29. An instrument accordingto claim 16, further comprising an integrated spotlight for illuminatingthe leveling rod.
 30. An instrument according to claim 29, wherein alight source of the spotlight is a laser diode.